The Composition And Distribution Characteristics Of The Biogenic Sedimentary Structures In The Tidal Flat Of The Yellow River Delta

Delta is the product of the interaction of river and receiving basin,which is affected by river input,tide,wave,structure and climate,etc.It is a significance sedimentary facies and an important place for oil and gas accumulation,with complex sedimentary environment combination and sedimentary characteristics.At present,most studies on deltas focus on physical and chemical deposition.With more than 200 years of research history,Ichnology has played an extremely important role in the identification and interpretation of sedimentary environment by analyzing biogenic sedimentary structures and reflecting the interaction between organisms and the environment.Therefore,the tidal flat of the Yellow River Delta was selected for the study of modern sedimentology and ichnology.The sedimentary environment,the typical species of trace-making organisms,and the composition and distribution of the modern biogenic sedimentary structures were observed and analyzed.Meantime,we tested and analyzed the sediment of the tidal flat of the YRD,including sediment grain size,total organic carbon content(TOC),salinity,turbidity,as well as environmental factors such as sediment bottom properties,hydrodynamics,deposition rate,and so on.These factors affect the composition and distribution of modern ichnocoenosis in the tidal flat of the Yellow River Delta.In addition,the characteristics of sedimentary environment and biogenic traces were studied,comparing with the composition and distribution characteristics of biogenic traces in the tidal flat of the YRD.The following progresses have been made:(1)There are ten species of trace makers in the tidal flat of the Yellow River Delta,which create a variety of biological traces,including trackways,crawling trails,feeding trails,dwelling traces,excretion traces,bird footprint and various forms of burrows in the bottom layer.The composition and distribution characteristics of these biological relics are significantly different in the supratidal,intertidal and subtidal zones of the Yellow River Deltaic tidal flat.(2)By comparing the composition and distribution characteristics of modern biological traces in the Pearl River Deltaic tidal flat,it is found that there are four species of trace makers in the Pearl River Delta,which are distributed in the intertidal zone.They create a variety of biological traces,including trackways,crawling trails,dwelling traces,excretion traces,bird footprint and various forms of burrows in the bottom layer.(3)The common typical trace makers of the two study areas were analyzed in detail,Macrophthalmus japonicus and Perinereis aibuhiteusis.Macrophthalmus japonicus is mainly distributed in the supratidal zone and intertidal zone of the tidal flat of the YRD with Y-shape,U-shape and L-shape and distributed in intertidal zone of the Pearl River Delta with Y-shape and I-shape.There was a great difference in the distribution range of Perinereis aibuhiteusis between the two study areas,which is distributed in the on both sides of tidal channel with strong hydrodynamic force in tidal flat of YRD and the other is in the area of weak hydrodynamic force in the Pearl River Delta.The abundance and diversity of biogenic traces are roughly the same,however,the characteristics of burrows in the layers are vary greatly.(4)It is found that sediment grain size,hydrodynamics,sedimentation rate and total organic carbon content had important effects on the abundance and diversity of the biogenic organisms and their traces,while salinity and turbidity had direct effects on the distribution of the species,thus affecting the distribution of their biogenic sedimentary structure.This study will supplement,perfect and revise the existing data of deltaic tidal flat neoichnology and modern tidal flat sedimentology.It also plays a certain role in interpreting and correcting the ancient tidal flat environment with high accuracy.Meantime,it provides modern biological empirical data for the detailed study of the morphological and ecological characteristics of crab and nereworm trace fossils and factors affecting their distribution.There are 31 pictures,8 tables and 123 references.